Sciency Words A to Z: The Drake Equation

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, D is for:


In 1961, American astronomer Frank Drake proved that alien life exists.  He didn’t do this with a telescope or by analyzing a Martian meteorite. No, Frank Drake proved it with math, pure and simple.  Or at least that’s the impression some people seem to get when they first hear about the Drake equation.

The Drake equation was first presented in 1961 at a conference held at the Green Bank Telescope in West Virginia. Only ten people were in the audience when Drake gave his presentation (one of those ten people, by the way, was a young Carl Sagan).  And the topic to be discussed at this conference: a new and highly controversial idea called SETI.

In this article from Universe Today, Drake is quoted explaining what inspired his equation:

As I planned the meeting, I realized a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it’s going to be to detect extraterrestrial life.  And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy.

After reading All These Worlds Are Yours by Jon Willis, I’ve come to think of the Drake equation as a to-do list for astrobiologists.

N = R* · fp · ne · fl · fi · fc · L
  • Figure out how many stars are born in our galaxy per year (R*).
  • Figure out how many of those stars have planets (fp).
  • Figure out how many of those planets could support life (ne).
  • Figure out how many planets that could support life actually do (fl).
  • Figure out how often life evolves into intelligent life (fi).
  • Figure out how often intelligent life develops radio communications that we could detect (fc).
  • Figure out how long the average intelligent civilization keeps its radio equipment working (L).

Like I said, it’s a to-do list.  It’s presented in the form of an equation because… well, you know… scientists.

At this point, we have a pretty good feel for the first two variables in the Drake equation.  As stated in this article from Astronomy Magazine, 1.5 to 3 new stars are born per year in our galaxy, and each star has at least one planet, on average.  Current and upcoming missions should start to pin down real numbers for the number of planets that could potentially support life.

Beyond that, those questions do get progressively harder, but astrobiologists are steadily working their way down their to-do list—or rather, they’re working their way through the equation, starting from the left and heading to the right.  Answers are coming, slowly but surely.

Next time on Sciency Words A to Z, when astrobiologists talk about Earth-like planets, what exactly does that mean?

6 thoughts on “Sciency Words A to Z: The Drake Equation

  1. These astrobiologist do seem to be going through a lot of trouble in figuring out if we are alone. A random thought popped into my head, what when you excluded earth some part of that equation, say fi, is zero. Cause everything here was a one time accident. Ok. Not sure if I make sense, but that sounded very important in my head

    Liked by 1 person

    1. Oh I absolutely get what you’re saying. There’s a lot of scientific literature out there about that. If any one part of the Drake equation turns out to be close to zero, then that’s it—we’re probably alone in the universe, or maybe the nearest alien civilization is so far away that we may as well be alone.

      With the first two variables, though, the numbers turned out to be fairly high. And the fact that we’ve already found a few planets that can be called “Earth-like” seems promising to me that the third number will also turn out to be fairly high. But there are still a lot more variables to work our way through, so we’ll see!


    1. On average, each star has at least one planet. Some starts might still have none, while others like our own Sun pump the average up. But still, it turns out there are a whole lot of planets out there, which bodes well for the prospect of finding alien life.

      And there are also rogue planets—planets that got thrown out of their original solar systems and now wander the galaxy all by themselves.


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